Methods and apparatus to compensate for radar system calibration changes

ABSTRACT

Methods, apparatus, systems and articles of manufacture to compensate radar system calibration are disclosed. A radio-frequency (RF) subsystem having a transmit channel, a receive channel, and a loopback path comprising at least a portion of the transmit channel and at least a portion of the receive channel, a loopback measurer to measure a first loopback response of the RF subsystem for a first calibration configuration of the RF subsystem, and to measure a second loopback response of the RF subsystem for a second calibration configuration of the RF subsystem, and a compensator to adjust at least one of a transmit programmable shifter or a digital front end based on a difference between the first loopback response and the second loopback response to compensate for a loopback response change when the RF subsystem is changed from the first calibration configuration to the second calibration configuration.

RELATED APPLICATION

This patent claims priority to Indian Provisional Patent Application No.201841040934, which was filed on Oct. 26, 2018. Indian ProvisionalPatent Application No. 201841040934 is hereby incorporated herein byreference in its entirety.

FIELD OF THE DISCLOSURE

This disclosure relates generally to radar systems, and, moreparticularly, to methods, apparatus, and articles of manufacture tocompensate radar system calibration changes.

BACKGROUND

Radar systems use radio frequency (RF) waves to determine the range,angle, and/or velocity of objects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate an example radar system constructed inaccordance with teachings of this disclosure.

FIG. 2 is a flowchart representative of example hardware logic ormachine-readable instructions for implementing the example radar systemof FIG. 1 to compensate for radar system calibration changes.

FIG. 3 illustrates another example radar system constructed inaccordance with teachings of this disclosure.

FIG. 4 is a flowchart representative of example hardware logic ormachine-readable instructions for implementing the example radar systemof FIG. 3 to compensate for radar system calibration changes.

FIG. 5 illustrates an example processor platform structured to executethe example machine-readable instructions of FIG. 2 and/or FIG. 4 toimplement the example radar systems of FIG. 1 and/or FIG. 3.

In general, the same reference numbers will be used throughout thedrawing(s) and accompanying written description to refer to the same orlike parts. Connecting lines or connectors shown in the various figurespresented are intended to represent example functional relationshipsand/or physical or logical couplings between the various elements.

DETAILED DESCRIPTION

To mitigate performance degradations resulting from, for example,temperature variations, radar RF/analog subsystem settings are variedbased on operating parameters such as temperature. The radar RF/analogsubsystem settings can be determined using calibration techniques.However, RF/analog subsystem settings changes resulting from calibrationcan instantaneously change a loopback response (e.g., a phase response,an amplitude response, etc.) of the radar RF/analog subsystem. Becausetracking algorithms rely on phase information across time and/or acrosssets of chirps, calibration changes and attendant loopback responsechanges can disturb ongoing object tracking. Thus, calibration cannot bedone during operation of some radar systems.

A loopback response represents the change in amount, type, shape, form,etc. of amplitude, phase, etc. a transmit signal undergoes between afirst point in a transmit signal path and a second point in a receivesignal path. In some examples, the first point is a point at which ananalog transmit signal is generated, and the second point is the pointat which an analog receive signal is converted to the digital domain. Indisclosed examples, the first point and the second point are selected toencompass portions of a transmit path and a receive path that changesufficiently based on calibration changes to warrant compensation. Forexample, all of a transmit analog signal path and all of a receiveanalog signal path may be included in a loopback path.

To compensate for RF/analog subsystem response changes resulting fromcalibration, examples disclosed herein determine: (a) a current loopbackresponse of the RF/analog subsystem for a current calibration, and (b) anew loopback response of the RF/analog subsystem for a new calibration.Differences between the current loopback response and the new loopbackresponse are used to digitally compensate for the RF/analog responsechanges resulting from calibration changes. Having compensated for theRF/analog subsystem response changes resulting from calibration, thecalibration setting can be changed without disturbing ongoing objecttracking (e.g., without disturbing and/or resetting tracking filters).

An example digital compensation includes the adjustment of thecoefficient(s) of a receive filter, a transmit filter, etc. such asthose found in a radar system. In some examples, the coefficient(s) aretrained so a particular QPSK symbol is received with a desired amplitudeand phase. If a calibration change is made, the same QPSK symbol wouldinstead be received with a different amplitude and phase. Thedifference(s) in amplitude and phase represent a change in loopbackresponse resulting from the calibration change. An example digitalcompensation would be a change in the filter coefficient(s) so the sameQPSK symbol is to be received with the desired amplitude and phase afterthe calibration change is made. An example compensation in a radarsystem modifies the amplitude and/or phase of a receiver output signalby determined amount. For example, by multiplying a receiver output by afactor A*exp(j*θ) to change the amplitude of the receiver output by anamount A, and the phase of the receiver output by a factor θ (e.g.,expressed in radians, where 2*π radians is 360 degrees), and j=sqrt(−1).Another example compensation in a radar system modifies an amplitudeand/or phase of a transmitter output signal by determined amount. Forexample, a transmitter input signal can be multiplied by a factorB*exp(j*θ) (e.g., to change the phase of the transmitter output by θradians). The multiplications can be carried out in a digital domain, anRF-analog-digital-mixed domain, etc. In the digital domain, themultiplications may be expressed as:

(I+j*Q)*A*exp(j*θ)=A*I*cos(θ)−A*Q*sin(θ)+j*A*Q*cos(θ)+j*A*I*sin(θ).

where I and Q are, respectively the real and imaginary receiver outputsor transmitter inputs.

In some examples, the loopbacks are performed using an internal transmit(TX) to receive (RX) loopback path in a radar system-on-a-chip (SoC)device. In some examples, the loopbacks are performed across radar SoCdevices to compensate for TX and/or common mode path changes. In someexamples, the loopbacks are performed in a test mode. In some examples,loopbacks are performed continuously at a known intermediate frequency(IF) frequency above the IF used for object tracking to continuouslytrack changes in the response of the radar RF/analog subsystem.

Reference will now be made in detail to non-limiting examples, some ofwhich are illustrated in the accompanying drawings.

FIGS. 1A and 1B are a block diagram of an example radar system 100configured to compensate for configuration changes resulting fromcalibration. The radar system 100 includes an example RF/analogsubsystem 102, an example digital signal processor (DSP) subsystem 104,and an example processor 106. In the illustrated example, the RF/analogsubsystem 102, and the DSP subsystem 104 are part of a radar SoC device.The processor 106, which may be part of a radar SoC device, is aprocessor on which a customer can implement customer-specificfunctionality.

To generate transmit signals, the RF/analog subsystem 102 includes anexample RF synthesizer 108. The RF synthesizer 108 of FIG. 1B generatesan RF transmit signal 110 from chirp control data 112 received from anexample timing engine 114 and, in some examples, from chirp control data116 received from a transmitter 118. Based on chirp parameter values fora sequence of chirps in a radar frame, the timing engine 114 generateschirp control signals that control the transmission and reception of thechirps in a frame based on the parameter values. In some examples, theRF synthesizer 108 includes a phase locked loop (PLL) and a voltagecontrolled oscillator (VCO).

To transmit the RF transmit signal 110, the RF/analog subsystem 102includes one or more transmit channels, one of which is designated atreference numeral 120, and one or more antennas for respective ones ofthe transmit channels 120, one of which is designated at referencenumeral 122. The transmit channels 120 each include an example pre-poweramplifier (PPA) 124, an example transmit programmable shifter 126, andan example power amplifier (PA) 128. The PPA 124 of FIG. 1A is coupledto the RF synthesizer 108 of FIG. 1B to receive the RF transmit signal110, and forms an amplified signal 130. The programmable shifter 126 ofFIG. 1A is coupled to the PPA 124 to receive the amplified signal 130,and forms a shifted signal 132. The PA 128 of FIG. 1A is coupled to theprogrammable shifter 126 to receive the shifted signal 132, and forms aradar transmit signal 134. The radar transmit signal 134 is emitted(e.g., transmitted) by the example antenna 122 of FIG. 1A. In someexamples, the programmable shifter 126 is configurable for bothfrequency and phase shifting. For example, the shifted signal 132 mayhave a frequency equal to the input frequency of the amplified signal130 plus a programmable offset frequency, and a phase equal to the inputphase of the amplified signal 130 plus a programmable offset phase. Insome examples, the transmit signal used to measure a loopback is an RFsignal (e.g., near 80 GHz) modulated by a sinusoidal oscillating signal(e.g., near 1 MHz), a square wave signal (e.g., near 1 MHz), etc.Loopback measurements are performed during time intervals when normaltransmitting and receiving is performed.

To receive an RF signal, the RF/analog subsystem 102 includes one ormore receive channels, one of which is designated at reference numeral136, and one or more antennas for respective ones of the receivechannels 136, one of which is designated at reference numeral 138. Thereceive channels 136 each include an example low-noise amplifier (LNA)140, an example mixer 142, an example intermediate frequency amplifier(IFA) 144, and an example analog-to-digital converter (ADC) 146. The LNA140 of FIG. 1A amplifies a radar return signal 148 received from theantenna 138 of FIG. 1A to form an RF receive signal 150. The mixer 142of FIG. 1B mixes the RF transmit signal 110 generated by transmissiongeneration circuitry (e.g., the RF synthesizer 108 and the timing engine114) with the RF receive signal 150 to generate an analog IF outputsignal 152. The mixer 142 is a down converter that generates the outputsignal 152 with a frequency equal to the difference between thefrequency of the signal 150 received from the LNA 140 and the frequencyof the signal 110 received from the transmission generation circuitry,both of which are RF signals. The IFA 144 of FIG. 1B (e.g., a combinedbandpass filter (BPF) and variable amplitude amplifier (VAA)) amplifiesthe analog IF output signal 152 to form an amplified analog IF signal154. The ADC 146 of FIG. 1B converts the amplified analog IF signal 154to the digital domain as a digital IF signal 156 (output signal 156 ofthe ADC 146).

The receive channels 136 are coupled to an example digital front end(DFE) 158 of the example DSP subsystem 104. The DFE 158 of FIG. 1Bperforms decimation filtering on the digital IF signal 156, DC offsetremoval, digital compensation of non-idealities in the receive channel136 (e.g., an inter-RX amplitude imbalance non-ideality, an inter-RXphase imbalance non-ideality, etc.), etc. The DFE 158 transfersdecimated digital IF signals 160 to a main processing unit 162 when theradar system 100 is in normal mode. In a loopback mode, the DFE 158transfers the decimated digital IF signals 160 to an example loopbackmeasurer 164.

To measure loopback responses, the DSP subsystem 104 of FIG. 1B includesthe loopback measurer 164. The loopback measurer 164 of FIG. 1B measuresthe phase and amplitude response of a loopback path. An example loopbackpath for the radar system 100 includes the transmit channel 120, anexample loopback channel 166, and the receive channel 136. The loopbackmeasurer 164 of FIG. 1B implements any number and/or type(s) of methods,algorithms, etc. to determine the response (e.g., amplitude and phase)of the loopback path based on changes to a known RF transmit signal 110as the RF transmit signal 110 passes through the transmit channel 120,the loopback channel 166, the receive channel 136, and is received asthe receive signal 156. Because the loopback measurer 164 receives theRF transmit signal 110 as a reference, the loopback measurer 164 candetermine what changes the RF transmit signal 110 underwent prior tobecoming the receive signal 156. Example methods and apparatus tomeasure loopback responses are disclosed in U.S. patent application Ser.No. 14/870,129, entitled “Measurement of Transceiver PerformanceParameters In a Radar System,” and filed on Sep. 30, 2015. U.S. patentapplication Ser. No. 14/870,129 is hereby incorporated herein byreference in its entirety.

The loopback channel 166 of FIGS. 1A and 1B includes an example combiner168, an example frequency shifter 170, and an example splitter 172. Thecombiner 168 of FIG. 1A receives the shifted signal 134 output by eachof the PAs 128, and forms a combined signal 174 from the shifted signals134. The combiner 168 provides the combined signal 174 to the frequencyshifter 170. The frequency shifter 170 of FIG. 1A applies a frequencyshift to the combined signal 174 using, for example, an on-off keying(OOK) modulator or a binary phase shift keying (BPSK) modulator to forma shifted combined signal 176. The frequency shifter 170 is coupled tothe splitter 172 to provide the shifted combined signal 176 to thesplitter 172. The splitter 172 of FIG. 1A is coupled to each of thereceive channels 136. The splitter 172 splits the shifted combinedsignal 176 to provide signals of equal power and phase to each of thereceive channels 136. In some examples, the splitter 172 splits theshifted combined signal 176 so the amplitude, attenuation, and/or delayon the signal from the splitter input 178 to the LNAs 140 of each of thereceive channels 136 are significantly similar.

To determine the range, angle, and/or velocity of an object, the exampleDSP subsystem 104 includes an example tracking system 180. The trackingsystem 180 of FIG. 1B implements any number and/or type(s) of methods,algorithms, etc. to determine the range, angle, and/or velocity of anobject based on the radar return signal 148 processed through thereceive channel 136. In the illustrated example, the tracking system 180is implemented as machine readable instructions executed on the mainprocessing unit 162.

To calibrate the RF/analog subsystem 102, the example DSP subsystem 104includes an example calibrator 182. The example calibrator of FIG. 1Bimplements any number and/or type(s) of methods, algorithms, etc. totake calibration measurements that characterize the RF/analog subsystem102 based on the chirp control data 112, 116, and to determinecalibration settings for the RF/analog subsystem 102 based on themeasurements. The calibrator 182 can compute new calibration settings astemperature changes occur to track temperature-based changes to circuitcharacteristics. In some examples, the calibrator 182 periodicallyand/or aperiodically determines calibration settings. Additionally,and/or alternatively, the calibrator 182 determines calibration settingsunder the control of the main processing unit 162 and/or the processor106. In the illustrated example, the calibrator 182 is implemented asmachine readable instructions executed on the main processing unit 162.In a calibration mode, the DFE 158 transfers the decimated digital IFsignals 160 to the calibrator 182.

To configure the RF/analog subsystem 102, the example DSP subsystemincludes an example configurer 184. The configurer 184 writesconfiguration (e.g., calibration) data, parameters, settings, etc.stored in a configuration data store 186 to the RF/analog subsystem 102to change the configuration of the RF/analog subsystem 102. Theconfiguration data store 186 may be any number and/or type(s) ofnon-transitory computer-readable storage device or disk.

As shown in FIG. 1B, the configuration data store 186 includes settingsfor a current (e.g., old) calibration configuration for the transmitchannel TX_OLD, a new calibration configuration for the transmit channelTX_NEW, a current (e.g., old) calibration configuration for the receivechannel RX_OLD, and a new calibration configuration for the receivechannel RX_NEW. The calibration configurations TX_OLD, TX_NEW, RX_OLDand RX_NEW can be determined by the calibrator 182. In examplesdisclosed herein, calibration configurations may include parameters suchas gain and/or phase jumps to be applied. The new calibrationconfigurations TX_NEW and RX_NEW can be associated with a differenttemperature than the other calibration configurations TX_OLD and RX_OLD.

Changes in configuration (e.g., calibration) data, parameters, settings,etc. applied to the RF/analog subsystem 102 can cause changes (e.g.,instantaneous changes) in the responses, characteristics, performance,etc. of the RF/analog subsystem 102. An example configuration change isfrom a first calibration configuration to a second calibrationconfiguration. Because such changes in calibration configuration canchange loopback response, such changes can disrupt the ability to trackone or more objects and/or the performance of object tracking performedby the tracking system 180. In some examples, such changes can require areset of the tracking system 180, which could disrupt the ongoingoperation of a system including the radar system 100.

To compensate for changes in the RF/analog subsystem 102 resulting from,for example, calibration changes, the example DSP subsystem 104 includesan example compensator 188. The compensator 188 changes the settings,coefficients, etc. of transmit and/or receive components at a change incalibration configuration so other receive components are not impactedby the change in calibration configuration that occurred. Thecompensator 188 of FIG. 1B controls the configurer 184 to configure theRF/analog subsystem 102 with a first calibration configuration C1, andcontrols the loopback measurer 164 to compute a first loopback responseL1 for the first calibration configuration C1. The compensator 188 ofFIG. 1B then controls the configurer 184 to configure the RF/analogsubsystem 102 with a second calibration configuration C2, and controlsthe loopback measurer 164 to compute a second loopback response L2 forthe second calibration configuration C2. The compensator 188 computesthe instantaneous change in loopback response by computing, for example,a difference between the loopback response L1 and the loopback responseL2. To compensate for the difference, the compensator 188 adjusts theparameters, settings, variables, etc. of the programmable shifters 126,the DFE 158, and/or the tracking system 180. Table 1 shows examplecombinations to compensate for TX and/or RX calibration configurationchanges. For example, to compensate for an RX amplitude and/or phasedifference resulting from a calibration change: a first loopback L1 isdetermined for a TX_OLD, RX_OLD calibration configuration, and a secondloopback L2 is determined for a TX_OLD RX_NEW calibration configuration,and compensation is performed by digitally changing settings of the DFE158 and/or the tracking system 180 based on a difference of L1 and L2.

TABLE 1 Loopback Configurations Where Configuration Loopback RX or TX tocompensate TX_OLD, RX_OLD L1 RX ΔA and/ DFE 158, and/or TX_OLD, RX_NEWL2 or Δθ tracking system 180 TX_OLD, RX_OLD L1 TX ΔA and/ ProgrammableTX_NEW, RX_OLD L2 or Δθ shifters 126, DFE 158, and/or tracking system180

In some examples, compensation is not applied during loopbackmeasurements and, as a result, the raw analog gain/phase change factorsfor the section is measured. Example methods and apparatus to measureloopback responses are disclosed in U.S. patent application Ser. No.14/870,129, entitled “Measurement of Transceiver Performance ParametersIn a Radar System,” and filed on Sep. 30, 2015. U.S. patent applicationSer. No. 14/870,129 is hereby incorporated herein by reference in itsentirety.

In some examples, an output 156 of the ADC 146 is expressed as I+jQ, anddigital compensation is performed by multiplying the output 156 of theADC 146 by a compensation factor A*exp(j*θ). If the compensation factorwas A₁*exp(j*θ₁) for a previous (e.g., old) calibration setting, thecompensation factor after a calibration setting change would beA₁*ΔA*exp(j*θ₁+Δθ), where ΔA and Δθ are the amplitude and phase changes,respectively, of the loopback due to the change in calibration. Theamplitude change ΔA is measured in digital amplitude levels, not inpower or log-scale. For example, if a first measurement is A1 and asecond measurement is A2, then the amplitude difference is A2/A1 and notA2−A1. If instead, log or power scale is used, the amplitude differencemay be represented by A2−A1. The phase difference is θ₁-θ₂. In someexamples, the TX compensation can be performed by multiplying the phaseshift applied by the TX programmable shifter 126 and an amplitudedifference and/or phase difference.

While an example RF/analog subsystem 102 is shown in FIGS. 1A and 1B,RF/analog subsystems according to other architectures having a loopbackchannel can be used. Other example RF/analog subsystems are disclosed inU.S. patent application Ser. No. 14/870,129, entitled “Measurement ofTransceiver Performance Parameters In a Radar System,” and filed on Sep.30, 2015. U.S. patent application Ser. No. 14/870,129 is herebyincorporated herein by reference in its entirety. Further, while twotransmit channels 120 and four receive channels 136 are shown in FIGS.1A and 1B, an RF/analog subsystem may have other numbers of transmitchannels and/or receive channels

While an example radar system 100 is illustrated in FIGS. 1A and 1B, oneor more of the elements, processes and/or devices illustrated in FIGS.1A and 1B may be combined, divided, re-arranged, omitted, eliminatedand/or implemented in any other way. Further, the example RF synthesizer108, the example timing engine 114, the example transmitter 118, theexample transmit channels 120, the example antennas 122, the example PPA124, the example programmable shifter 126, the example PA 128, thereceive channels 136, the example antennas 138, the example LNA 140, theexample mixer 142, the example IFA 144, the example ADC 146, the exampleDFE 158, the example main processing unit 162, the example loopbackmeasurer 164, the example loopback channel 166, the example combiner168, the example frequency shifter 170, the example splitter 172, theexample tracking system 180, the example calibrator 182, the exampleconfigurer 184, the example configuration data store 186, the examplecompensator 188 and/or, more generally, the example radar system 100 ofFIGS. 1A and 1B may be implemented by hardware, software, firmwareand/or any combination of hardware, software and/or firmware. Thus, forexample, any of the example RF synthesizer 108, the example timingengine 114, the example transmitter 118, the example transmit channels120, the example antennas 122, the example PPA 124, the exampleprogrammable shifter 126, the example PA 128, the receive channels 136,the example antennas 138, the example LNA 140, the example mixer 142,the example IFA 144, the example ADC 146, the example DFE 158, theexample main processing unit 162, the example loopback measurer 164, theexample loopback channel 166, the example combiner 168, the examplefrequency shifter 170, the example splitter 172, the example trackingsystem 180, the example calibrator 182, the example configurer 184, theexample configuration data store 186, the example compensator 188and/or, more generally, the example radar system 100 of FIGS. 1A and 1Bcould be implemented by one or more analog or digital circuit(s), logiccircuits, programmable processor(s), programmable controller(s),graphics processing unit(s) (GPU(s)), digital signal processor(s)(DSP(s)), application specific integrated circuit(s) (ASIC(s)),programmable logic device(s) (PLD(s)), field programmable gate array(s)(FPGA(s)), and/or field programmable logic device(s) (FPLD(s)). Whenreading any of the apparatus or system claims of this patent to cover apurely software and/or firmware implementation, at least one of theexample RF synthesizer 108, the example timing engine 114, the exampletransmitter 118, the example transmit channels 120, the example antennas122, the example PPA 124, the example programmable shifter 126, theexample PA 128, the receive channels 136, the example antennas 138, theexample LNA 140, the example mixer 142, the example IFA 144, the exampleADC 146, the example DFE 158, the example main processing unit 162, theexample loopback measurer 164, the example loopback channel 166, theexample combiner 168, the example frequency shifter 170, the examplesplitter 172, the example tracking system 180, the example calibrator182, the example configurer 184, the example configuration data store186, the example compensator 188 and/or the example radar system 100is/are hereby expressly defined to include a non-transitorycomputer-readable storage device or storage disk such as a memory, adigital versatile disk (DVD), a compact disc (CD), a compact discread-only memory (CD-ROM), a Blu-ray disk, etc. including the softwareand/or firmware. Further still, the example radar system 100 of FIGS. 1Aand 1B may include one or more elements, processes and/or devices inaddition to, or instead of, those illustrated in FIGS. 1A and 1B, and/ormay include more than one of any or all of the illustrated elements,processes and devices. As used herein, the phrase “in communication,”including variations thereof, encompasses direct communication and/orindirect communication through one or more intermediary components, anddoes not require direct physical (e.g., wired) communication and/orconstant communication, but rather additionally includes selectivecommunication at periodic intervals, scheduled intervals, aperiodicintervals, and/or one-time events.

A flowchart representative of example hardware logic, machine-readableinstructions, hardware implemented state machines, and/or anycombination thereof for implementing the radar system 100 of FIGS. 1Aand 1B is shown in FIG. 2. The machine-readable instructions may be anexecutable program or portion of an executable program for execution bya computer processor such as the processor 502 shown in the exampleprocessor platform 500 discussed below in connection with FIG. 5. Theprogram may be embodied in software stored on a non-transitorycomputer-readable storage medium such as a CD, a CD-ROM, a floppy disk,a hard drive, a DVD, a Blu-ray disk, or a memory associated with theprocessor 502, but the entire program and/or parts thereof couldalternatively be executed by a device other than the processor 502and/or embodied in firmware or dedicated hardware. Further, although theexample program is described with reference to the flowchart illustratedin FIG. 2, many other methods of implementing the example radar system100 may alternatively be used. For example, the order of execution ofthe blocks may be changed, and/or some of the blocks described may bechanged, eliminated, or combined. Additionally, and/or alternatively,any or all of the blocks may be implemented by one or more hardwarecircuits (e.g., discrete and/or integrated analog and/or digitalcircuitry, an FPGA, an ASIC, a PLD, an FPLD, a comparator, anoperational-amplifier (op-amp), a logic circuit, etc.) structured toperform the corresponding operation without executing software orfirmware.

The program of FIG. 2 begins at block 202, where the configurer 184configures the RF/analog subsystem 102 with the TX_OLD and the RX_OLDcalibration configurations (block 202). The example loopback measurer164 measures a first loopback, which includes a phase PHASE1 and anamplitude AMP1 (block 204). In FIGS. 1A and 1B the loopback pathincludes the transmit channel 120, the loopback channel 166, and thereceive channel 136. In FIGS. 1A and 1B, the transmit channel 120 isconfigured to obtain the RF transmit signal 110 to be transmittedthrough the loopback channel 166, into the receive channel 136, and tobe measured by the loopback measurer 164. The configurer 184 configuresthe RF/analog subsystem 102 with the TX_OLD and the RX_NEW calibrationconfigurations (block 206). The loopback measurer 164 measures a secondloopback, which includes a phase PHASE2 and an amplitude AMP2 (block208). The compensator 188 computes a first phase difference Δθ_1=θ₂−θ₁,and a first amplitude difference ΔA_1=A₂/A₁ (block 210). The configurer184 configures the RF/analog subsystem 102 with the TX_NEW and theRX_OLD calibration configurations (block 212). The loopback measurer 164measures a third loopback, which includes a phase θ₃ and an amplitude A₃(block 214). The compensator 188 computes a second phase differenceΔθ_2=θ₃−θ₁, and a second amplitude difference ΔA_2=A₃/A₁ (block 216).The compensator 188 compensates for the first phase difference Δθ_1, thefirst amplitude difference ΔA_1, the second phase difference Δθ_2, andthe second amplitude difference ΔA_2 by adjusting the parameters,settings, variables, etc. of the programmable shifters 126, the DFE 158,and/or the tracking system 180 (block 218).

While TX and RX amplitude and phase differences can be identified andcompensated in the illustrated example of FIG. 1, the radar system 100may not be able to identify amplitude and/or phase differences on acommon mode path.

FIG. 3 is a block diagram of another radar system 300 constructed inaccordance with aspects of this disclosure that can identify amplitudeand/or phase differences on a common mode path using antenna couplingbetween antennae of different radar systems. The example radar system300 of FIG. 2 includes two separate radar systems 302 and 304, such astwo of the radar system 100 of FIGS. 1A and 1B. In the illustratedexample of FIG. 3, a loopback channel 306 includes the transmit channel120 of the radar system 302, a loopback transmission path 308 betweenthe antenna 122 of the radar system 302 and the antenna 138 of the radarsystem 304, and the receive channel 136 of the radar system 304. Theloopback transmission path 308 includes, for example, electro-magneticcoupling, reflections of radar signals by surfaces of a mechanicalhousing, etc. In the illustrated example, a common local oscillator(e.g., the RF synthesizer 108) is used by the transmit channel 120 ofthe radar system 302 and by the receive channel 136 of the radar system304. Use of the common local oscillator enables the loopback measurer164 to measure a loopback between the radar system 302 and the radarsystem 304. Using loopback measurements by the loopback measurer 164enables the compensator 188 to compensate changes in the transmitchannel 120 and/or a common mode path. To compensate for the changes,the compensator 188 adjusts the parameters, settings, variables, etc. ofthe programmable shifters 126, the DFE 158, and/or the tracking system180.

While an example manner of implementing the radar system 300 is shown inFIG. 3, one or more of the elements, processes and/or devicesillustrated in FIG. 3 may be combined, divided, re-arranged, omitted,eliminated and/or implemented in any other way. Further, the example RFsynthesizer 108, the example radar systems 302 and 304, the exampletransmit channel 120, the example receive channel 136, the example mixer142, the example DFE 158, the example loopback measurer 164, the exampleconfigurer 184, the example compensator 188 and/or, more generally, theexample radar system 300 of FIG. 3 may be implemented by hardware,software, firmware and/or any combination of hardware, software and/orfirmware. Thus, for example, any of the example RF synthesizer 108, theexample radar systems 302 and 304, the example transmit channel 120, theexample receive channel 136, the example mixer 142, the example DFE 158,the example loopback measurer 164, the example configurer 184, theexample compensator 188 and/or, more generally, the example radar system300 could be implemented by one or more analog or digital circuit(s),logic circuits, programmable processor(s), programmable controller(s),GPU(s), DSP(s), ASIC(s), PLD(s), FPGA(s), and/or FPLD(s). When readingany of the apparatus or system claims of this patent to cover a purelysoftware and/or firmware implementation, at least one of the example RFsynthesizer 108, the example radar systems 302 and 304, the exampletransmit channel 120, the example receive channel 136, the example mixer142, the example DFE 158, the example loopback measurer 164, the exampleconfigurer 184, the example compensator 188, and/or the example radarsystem 300 is/are hereby expressly defined to include a non-transitorycomputer-readable storage device or storage disk such as a memory, aDVD, a CD, a CD-ROM, a Blu-ray disk, etc. including the software and/orfirmware. Further still, the example radar system 300 of FIG. 3 mayinclude one or more elements, processes and/or devices in addition to,or instead of, those illustrated in FIG. 4, and/or may include more thanone of any or all of the illustrated elements, processes and devices.

A flowchart representative of example hardware logic, machine-readableinstructions, hardware implemented state machines, and/or anycombination thereof for implementing the radar system 300 of FIG. 3 isshown in FIG. 4. The machine-readable instructions may be an executableprogram or portion of an executable program for execution by a computerprocessor such as the processor 502 shown in the example processorplatform 500 discussed below in connection with FIG. 5. The program maybe embodied in software stored on a non-transitory computer-readablestorage medium such as a CD, a CD-ROM, a floppy disk, a hard drive, aDVD, a Blu-ray disk, or a memory associated with the processor 502, butthe entire program and/or parts thereof could alternatively be executedby a device other than the processor 502 and/or embodied in firmware ordedicated hardware. Further, although the example program is describedwith reference to the flowchart illustrated in FIG. 4, many othermethods of implementing the example radar system 300 may alternativelybe used. For example, the order of execution of the blocks may bechanged, and/or some of the blocks described may be changed, eliminated,or combined. Additionally, and/or alternatively, any or all of theblocks may be implemented by one or more hardware circuits (e.g.,discrete and/or integrated analog and/or digital circuitry, an FPGA, anASIC, a PLD, an FPLD, a comparator, an op-amp, a logic circuit, etc.)structured to perform the corresponding operation without executingsoftware or firmware.

The program of FIG. 4 begins at block 402, where the configurer 184configures the radar system 302 with the TX_OLD calibrationconfiguration, and configures the radar system 304 with the RX_OLDcalibration configuration (block 402). The loopback measurer 164measures a first loopback, which includes a phase θ₁ and an amplitude A₁(block 404). In FIG. 3 the loopback path includes the transmit channel120 of the radar system 302, the loopback transmission path 308 betweenthe antenna 122 of the radar system 302 and the antenna 138 of the radarsystem 304, and the receive channel 136 of the radar system 304. Theconfigurer 184 configures the radar system 302 with the TX_NEWcalibration configuration, and configures the radar system 304 with theRX_OLD calibration configuration (block 406). The loopback measurer 164measures a second loopback, which includes a phase θ₂ and an amplitudeAMP2 (block 408). The compensator 188 computes a phase differenceΔθ=θ₂−θ₁, and an amplitude difference ΔA=A₂−A₁ (block 410). Thecompensator 188 compensates for the phase difference Δθ, and theamplitude difference ΔA by adjusting the parameters, settings,variables, etc. of the DFE 158 (block 412).

In examples disclosed herein, phase correction for TX involvescompensating the shift in phase at TX path (say θ_(new)−θ_(old)) byadding this to the existing phase shifter correction (θ_(exist)).Therefore, the new correction to be configured isθ_(exist)+θ_(new)−θ_(old). Phase correction at RX involves compensatingthe shift in phase at RX path in a manner similar to the TX case.However, in some examples, such RX path correction is applied digitallyat the DFE 158 (e.g., after ADC samples are recorded). A gain correctionΔA_(new)=A_(old)/A_(new) is also applied. In some examples, such gaincorrection is processed digitally (e.g., at the DFE 158). Thetransformed ADC data is then computed asADC_data*ΔA_(exist)*ΔA_(new)*exp(j(θ_(exist)+θ_(new)−θ_(old))). Theamplitude shift is corrected at the TX power backoff in dB by adding (orsubtracting) the delta change in power during a settings update.

As mentioned above, the example processes of FIGS. 2 and 4 may beimplemented using executable instructions computer and/ormachine-readable instructions) stored on a non-transitory computerand/or machine-readable medium such as a hard disk chive, a flashmemory, a read-only memory, a CD, a CD-ROM, a DVD, a cache, arandom-access memory and/or any other storage device or storage disk inwhich information is stored for any duration (e.g., for extended timeperiods, permanently, for brief instances, for temporarily buffering,and/or for caching of the information). As used herein, the termnon-transitory computer-readable medium is expressly defined to includeany type of computer-readable storage device and/or storage disk and toexclude propagating signals and to exclude transmission media.

As used herein, when the phrase “at least” is used as the transitionterm in, for example, a preamble of a claim, it is open-ended in thesame manner as the term “comprising” and “including” are open ended. Theterm “and/or” when used, for example, in a form such as A, B, and/or Crefers to any combination or subset of A, B, C such as (1) A alone, (2)B alone, (3) C alone, (4) A with B, (5) A with C, (6) B with C, and (7)A with B and with C. As used herein in the context of describingstructures, components, items, objects and/or things, the phrase “atleast one of A and B” is intended to refer to implementations includingany of (1) at least one A, (2) at least one B, and (3) at least one Aand at least one B. Similarly, as used herein in the context ofdescribing structures, components, items, objects and/or things, thephrase “at least one of A or B” is intended to refer to implementationsincluding any of (1) at least one A, (2) at least one B, and (3) atleast one A and at least one B. As used herein in the context ofdescribing the performance or execution of processes, instructions,actions, activities and/or steps, the phrase “at least one of A and B”is intended to refer to implementations including any of (1) at leastone A, (2) at least one B, and (3) at least one A and at least one B.Similarly, as used herein in the context of describing the performanceor execution of processes, instructions, actions, activities and/orsteps, the phrase “at least one of A or B” is intended to refer toimplementations including any of (1) at least one A, (2) at least one B,and (3) at least one A and at least one B.

FIG. 5 is a block diagram of an example processor platform 500structured to execute the instructions of FIGS. 2 and 3 to implement theradar system 100 of FIGS. 1A and 1B, and the radar systems 300, 302 and304 of FIG. 3. The processor platform 500 can be, for example, anautomobile, a server, a personal computer, a workstation, a mobiledevice (e.g., a cell phone, a smart phone, a tablet such as an IPAD™), aheadset or other wearable device, or any other type of computing deviceimplementing radar.

The processor platform 500 of the illustrated example includes aprocessor 502. The processor 502 of the illustrated example is hardware.For example, the processor 502 can be implemented by one or moreintegrated circuits, logic circuits, microprocessors, GPUs, DSPs, orcontrollers from any desired family or manufacturer. The hardwareprocessor may be a semiconductor based (e.g., silicon based) device. Inthis example, the processor implements the example RF synthesizer 108,the example timing engine 114, the example transmitter 118, the exampletransmit channels 120, the example antennas 122, the example PPA 124,the example programmable shifter 126, the example PA 128, the receivechannels 136, the example antennas 138, the example LNA 140, the examplemixer 142, the example IFA 144 the example ADC 146, the example DFE 158,the example main processing unit 162, the example loopback measurer 164,the example loopback channel 166, the example combiner 168, the examplefrequency shifter 170, the example splitter 172, the example trackingsystem 180, the example calibrator 182, the example configurer 184, theexample configuration data store 186, and the example compensator 188.

The processor 502 of the illustrated example includes a local memory 504(e.g., a cache). The processor 502 of the illustrated example is incommunication with a main memory including a volatile memory 506 and anon-volatile memory 508 via a bus 510. The volatile memory 506 may beimplemented by Synchronous Dynamic Random Access Memory (SDRAM), DynamicRandom Access Memory (DRAM), RAMBUS® Dynamic Random Access Memory(RDRAM®) and/or any other type of random access memory device. Thenon-volatile memory 508 may be implemented by flash memory and/or anyother desired type of memory device. Access to the main memory 506, 508is controlled by a memory controller.

The processor platform 500 of the illustrated example also includes aninterface circuit 512. The interface circuit 512 may be implemented byany type of interface standard, such as an Ethernet interface, auniversal serial bus (USB), a Bluetooth® interface, a near fieldcommunication (NFC) interface, and/or a peripheral component interface(PCI) express interface.

In the illustrated example, one or more input devices 514 are connectedto the interface circuit 512. The input device(s) 514 permit(s) a userto enter data and/or commands into the processor 502. The inputdevice(s) can be implemented by, for example, an audio sensor, amicrophone, a camera (still or video), a keyboard, a button, a mouse, atouchscreen, a track-pad, a trackball, isopoint and/or a voicerecognition system.

One or more output devices 516 are also connected to the interfacecircuit 512 of the illustrated example. The output devices 516 can beimplemented, for example, by display devices (e.g., a light emittingdiode (LED), an organic light emitting diode (OLED), a liquid crystaldisplay (LCD), a cathode ray tube display (CRT), an in-place switching(IPS) display, a touchscreen, etc.), a tactile output device, a printerand/or speaker. The interface circuit 512 of the illustrated example,thus, typically includes a graphics driver card, a graphics driver chipand/or a graphics driver processor.

The interface circuit 512 of the illustrated example also includes acommunication device such as a transmitter, a receiver, a transceiver, amodern, a residential gateway, a wireless access point, and/or a networkinterface to facilitate exchange of data with external machines (e.g.,computing devices of any kind) via a network 518. The communication canbe via, for example, an Ethernet connection, a digital subscriber line(DSL) connection, a telephone line connection, a coaxial cable system, asatellite system, a line-of-site wireless system, a cellular telephonesystem, etc.

The processor platform 500 of the illustrated example also includes oneor more mass storage devices 520 for storing software and/or data.Examples of such mass storage devices 520 include floppy disk drives,hard drive disks, CD drives, Blu-ray disk drives, redundant array ofindependent disks (RAID) systems, and DVD drives.

Coded instructions 522 including the coded instructions of FIGS. 2 and 4may be stored in the mass storage device 520, in the volatile memory506, in the non-volatile memory 508, and/or on a removablenon-transitory computer-readable storage medium such as a CD-ROM or aDVD.

From the foregoing, it will be appreciated that example methods,apparatus and articles of manufacture have been disclosed thatcompensate for RF/analog TX and RX changes resulting from calibrationconfiguration changes. From the foregoing, it will be appreciated thatmethods, apparatus and articles of manufacture have been disclosed whichenhance the operations of a computer by allowing object tracking and/orcustomer algorithms to be performed without interruption resulting fromcalibration changes. The disclosed methods, apparatus and articles ofmanufacture improve the efficiency of using a computing device bymaintaining phase coherence across calibration intervals using internalloopbacks and/or loopbacks across cascaded radar devices. Moreover,performance of location and/or velocity tracking systems is improved asa result of the improved phase coherency across tracked frames.Furthermore, example methods, apparatus, and/or articles of manufacturedisclosed herein identify and overcome inaccuracies and inability in theprior art to perform object tracking. The disclosed methods, apparatusand articles of manufacture are accordingly directed to one or moreimprovement(s) in the functioning of a computer.

Example methods, apparatus, and articles of manufacture to compensateradar system calibration changes are disclosed herein. Further examplesand combinations thereof include at least the following.

Example 1 comprises a radar system, comprising a radio-frequency (RF)subsystem having a transmit channel, a receive channel, and a loopbackpath comprising at least a portion of the transmit channel and at leasta portion of the receive channel, a loopback measurer to measure a firstloopback response of the RF subsystem for a first calibrationconfiguration of the RF subsystem, and to measure a second loopbackresponse of the RF subsystem for a second calibration configuration ofthe RF subsystem, and a compensator to adjust at least one of a transmitprogrammable shifter or a digital front end based on a differencebetween the first loopback response and the second loopback response tocompensate for a loopback response change when the RF subsystem ischanged from the first calibration configuration to the secondcalibration configuration.

Example 2 comprises the radar system of example 1, wherein the radarsystem is a system-on-a-chip device.

Example 3 comprises the radar system of example 2, wherein the firstcalibration configuration of the RF subsystem comprises a currentcalibration configuration of the transmit channel, and a currentcalibration configuration of the receive channel, the second calibrationconfiguration is the current calibration configuration of the transmitchannel, and a new calibration configuration of the receive channel, andthe difference between the first loopback response and the secondloopback response represents a change in the receive channel.

Example 4 comprises the radar system of example 2, wherein the firstcalibration configuration of the RF subsystem comprises a currentcalibration configuration of the transmit channel, and a currentcalibration configuration of the receive channel, the second calibrationconfiguration is a new calibration configuration of the transmitchannel, and the current calibration configuration of the receivechannel, and the difference between the first loopback response and thesecond loopback response represents a change in the transmit channel.

Example 5 comprises the radar system of example 1, wherein the radarsystem comprises a first radar system-on-a-chip device that includes thetransmit channel and a second radar system-on-a-chip device thatincludes the receive channel.

Example 6 comprises the radar system of example 5, wherein the firstcalibration configuration of the RF subsystem is a current calibrationconfiguration of the transmit channel of the first radarsystem-on-a-chip device, and a current calibration configuration of thereceive channel of the second radar system-on-a-chip device, the secondcalibration configuration of the RF subsystem is a new calibrationconfiguration of the transmit channel of the first radarsystem-on-a-chip device, and the current calibration configuration ofthe receive channel of the second radar system-on-a-chip device, and thedifference between the first loopback response and the second loopbackresponse represents a change in at least one of the transmit channel ofthe first radar system-on-a-chip device, or a common mode path.

Example 7 comprises the radar system of example 6, wherein thecompensator is to adjust the digital front end based on the differencebetween the first loopback response and the second loopback response.

Example 8 comprises the radar system of example 1 wherein thecompensator adjusts the at least one of the transmit programmableshifter or the digital front end corresponding to multiplying a signaland the loopback response change.

Example 9 comprises the radar system of example 1, wherein the receivechannel comprises a low-noise amplifier, a mixer, an intermediatefrequency amplifier, and an analog-to-digital converter.

Example 10 comprises the radar system of example 1, wherein the transmitchannel comprises an RF synthesizer, a programmable shifter, and a poweramplifier.

Example 11 comprises the radar system of example 1, wherein the loopbackpath comprises a combiner, a frequency shifter, and a splitter.

Example 12 comprises a method, comprising measuring a first loopbackresponse of a radio-frequency (RF) subsystem for a first calibrationconfiguration of the RF subsystem, measuring a second loopback responseof the RF subsystem for a second calibration configuration of the RFsubsystem, and adjusting at least one of a transmit programmable shifteror a digital front end based on a difference between the first loopbackresponse and the second loopback response to compensate for a loopbackresponse change when the RF subsystem is changed from the firstcalibration configuration to the second calibration configuration.

Example 13 comprises the method of example 12, wherein the firstcalibration configuration of the RF subsystem comprises a currentcalibration configuration of a transmit channel, and a currentcalibration configuration of a receive channel, the second calibrationconfiguration is the current calibration configuration of the transmitchannel, and a new calibration configuration of the receive channel, andthe difference between the first loopback response and the secondloopback response represents a change in the receive channel.

Example 14 comprises the method of example 12, wherein the firstcalibration configuration of the RF subsystem comprises a currentcalibration configuration of a transmit channel, and a currentcalibration configuration of a receive channel, the second calibrationconfiguration is a new calibration configuration of the transmitchannel, and the current calibration configuration of the receivechannel, and the difference between the first loopback response and thesecond loopback response represents a change in the transmit channel.

Example 15 comprises the method of example 12, wherein the firstcalibration configuration of the RF subsystem is a current calibrationconfiguration of a transmit channel of a first system-on-a-chip device,and a current calibration configuration of a receive channel of a secondsystem-on-a-chip device, the second calibration configuration of the RFsubsystem is a new calibration configuration of the transmit channel ofthe first system-on-a-chip device, and the current calibrationconfiguration of the receive channel of the second system-on-a-chipdevice, and the difference between the first loopback response and thesecond loopback response represents a change in the transmit channel anda common mode path.

Example 16 comprises the method of example 12, wherein the firstcalibration configuration of the RF subsystem is a current calibrationconfiguration of a transmit channel of a first system-on-a-chip device,and a current calibration configuration of a receive channel of a secondsystem-on-a-chip device, the second calibration configuration of the REsubsystem is the current calibration configuration of the transmitchannel of the first system-on-a-chip device, and a new calibrationconfiguration of the receive channel of the second system-on-a-chipdevice, and the difference between the first loopback response and thesecond loopback response represents a change in the receive channel.

Example 17 comprises the method of example 12, wherein adjusting the atleast one of a transmit programmable shifter or a digital front endbased on a difference between the first loopback response and the secondloopback response comprises multiplying at least one of a transmitsignal or a receive signal, and the loopback response change.

Example 18 comprises a non-transitory computer-readable storage mediumcomprising instructions that, when executed, cause a machine to at leastmeasure a first loopback response of a radio-frequency (RF) subsystemfor a first calibration configuration of the RF subsystem, measure asecond loopback response of the RF subsystem for a second calibrationconfiguration of the RF subsystem, and adjust at least one of a transmitprogrammable shifter or a digital front end based on a differencebetween the first loopback response and the second loopback response tocompensate for a loopback response change when the RF subsystem ischanged from the first calibration configuration to the secondcalibration configuration.

Example 19 comprises the non-transitory computer-readable storage mediumof example 18, wherein the first calibration configuration of the RFsubsystem comprises a current calibration configuration of a transmitchannel, and a current calibration configuration of a receive channel,the second calibration configuration is the current calibrationconfiguration of the transmit channel, and a new calibrationconfiguration of the receive channel, and the difference between thefirst loopback response and the second loopback response represents achange in the receive channel.

Example 20 comprises the non-transitory computer-readable storage mediumof example 18, wherein the first calibration configuration of the RFsubsystem comprises a current calibration configuration of a transmitchannel, and a current calibration configuration of a receive channel,the second calibration configuration is a new calibration configurationof the transmit channel, and the current calibration configuration ofthe receive channel, and the difference between the first loopbackresponse and the second loopback response represents a change in thetransmit channel.

Example 21 comprises the non-transitory computer-readable storage mediumof example 18, wherein the first calibration configuration of the RFsubsystem is a current calibration configuration of a transmit channelof a first system-on-a-chip device, and a current calibrationconfiguration of a receive channel of a second system-on-a-chip device,the second calibration configuration of the RF subsystem is a newcalibration configuration of the transmit channel of the firstsystem-on-a-chip device, and the current calibration configuration ofthe receive channel of the second system-on-a-chip device, and thedifference between the first loopback response and the second loopbackresponse represents a change in at least one of the transmit channel, ora common mode path. It is noted that this patent claims priority toIndian Provisional Patent Application Serial No. 201841040934, which wasfiled on Oct. 26, 2018, and is hereby incorporated by reference in itsentirety.

Any references, comprising publications, patent applications, andpatents cited herein are hereby incorporated in their entirety byreference to the same extent as if each reference were individually andspecifically indicated to be incorporated by reference and were setforth in its entirety herein.

Although certain example methods, apparatus and articles of manufacturehave been disclosed herein, the scope of coverage of this patent is notlimited thereto. On the contrary, this patent covers all methods,apparatus and articles of manufacture fairly falling within the scope ofthe claims of this patent.

What is claimed is:
 1. A radar system, comprising: a radio-frequency(RF) subsystem having a transmit channel, a receive channel, and aloopback path comprising at least a portion of the transmit channel andat least a portion of the receive channel; a loopback measurer tomeasure a first loopback response of the RF subsystem for a firstcalibration configuration of the RF subsystem, and to measure a secondloopback response of the RF subsystem for a second calibrationconfiguration of the RF subsystem; and a compensator to adjust at leastone of a transmit programmable shifter or a digital front end based on adifference between the first loopback response and the second loopbackresponse to compensate for a loopback response change when the RFsubsystem is changed from the first calibration configuration to thesecond calibration configuration.
 2. The radar system of claim 1,wherein the radar system is a system-on-a-chip device.
 3. The radarsystem of claim 2, wherein the first calibration configuration of the RFsubsystem comprises a current calibration configuration of the transmitchannel, and a current calibration configuration of the receive channel,the second calibration configuration is the current calibrationconfiguration of the transmit channel, and a new calibrationconfiguration of the receive channel, and the difference between thefirst loopback response and the second loopback response represents achange in the receive channel.
 4. The radar system of claim 2, whereinthe first calibration configuration of the RF subsystem comprises acurrent calibration configuration of the transmit channel, and a currentcalibration configuration of the receive channel, the second calibrationconfiguration is a new calibration configuration of the transmitchannel, and the current calibration configuration of the receivechannel, and the difference between the first loopback response and thesecond loopback response represents a change in the transmit channel. 5.The radar system of claim 1, wherein the radar system comprises a firstradar system-on-a-chip device that includes the transmit channel and asecond radar system-on-a-chip device that includes the receive channel.6. The radar system of claim 5, wherein the first calibrationconfiguration of the RF subsystem is a current calibration configurationof the transmit channel of the first radar system-on-a-chip device, anda current calibration configuration of the receive channel of the secondradar system-on-a-chip device, the second calibration configuration ofthe RF subsystem is a new calibration configuration of the transmitchannel of the first radar system-on-a-chip device, and the currentcalibration configuration of the receive channel of the second radarsystem-on-a-chip device, and the difference between the first loopbackresponse and the second loopback response represents a change in atleast one of the transmit channel of the first radar system-on-a-chipdevice, or a common mode path.
 7. The radar system of claim 6, whereinthe compensator is to adjust the digital front end based on thedifference between the first loopback response and the second loopbackresponse.
 8. The radar system of claim 1, wherein the compensatoradjusts the at least one of the transmit programmable shifter or thedigital front end corresponding to multiplying a signal and the loopbackresponse change.
 9. The radar system of claim 1, wherein the receivechannel comprises a low-noise amplifier, a mixer, an intermediatefrequency amplifier, and an analog-to-digital converter.
 10. The radarsystem of claim 1, wherein the transmit channel comprises an RFsynthesizer, a programmable shifter, and a power amplifier.
 11. Theradar system of claim 1, wherein the loopback path comprises a combiner,a frequency shifter, and a splitter.
 12. A method, comprising: measuringa first loopback response of a radio-frequency (RF) subsystem for afirst calibration configuration of the RF subsystem; measuring a secondloopback response of the RF subsystem for a second calibrationconfiguration of the RF subsystem; and adjusting at least one of atransmit programmable shifter or a digital front end based on adifference between the first loopback response and the second loopbackresponse to compensate for a loopback response change when the RFsubsystem is changed from the first calibration configuration to thesecond calibration configuration.
 13. The method of claim 12, whereinthe first calibration configuration of the RF subsystem comprises acurrent calibration configuration of a transmit channel, and a currentcalibration configuration of a receive channel, the second calibrationconfiguration is the current calibration configuration of the transmitchannel, and a new calibration configuration of the receive channel, andthe difference between the first loopback response and the secondloopback response represents a change in the receive channel.
 14. Themethod of claim 12, wherein the first calibration configuration of theRF subsystem comprises a current calibration configuration of a transmitchannel, and a current calibration configuration of a receive channel,the second calibration configuration is a new calibration configurationof the transmit channel, and the current calibration configuration ofthe receive channel, and the difference between the first loopbackresponse and the second loopback response represents a change in thetransmit channel.
 15. The method of claim 12, wherein the firstcalibration configuration of the RF subsystem is a current calibrationconfiguration of a transmit channel of a first system-on-a-chip device,and a current calibration configuration of a receive channel of a secondsystem-on-a-chip device, the second calibration configuration of the RFsubsystem is a new calibration configuration of the transmit channel ofthe first system-on-a-chip device, and the current calibrationconfiguration of the receive channel of the second system-on-a-chipdevice, and the difference between the first loopback response and thesecond loopback response represents a change in the transmit channel anda common mode path.
 16. The method of claim 12, wherein the firstcalibration configuration of the RF subsystem is a current calibrationconfiguration of a transmit channel of a first system-on-a-chip device,and a current calibration configuration of a receive channel of a secondsystem-on-a-chip device, the second calibration configuration of the RFsubsystem is the current calibration configuration of the transmitchannel of the first system-on-a-chip device, and a new calibrationconfiguration of the receive channel of the second system-on-a-chipdevice, and the difference between the first loopback response and thesecond loopback response represents a change in the receive channel. 17.The method of claim 12, wherein adjusting the at least one of a transmitprogrammable shifter or a digital front end based on a differencebetween the first loopback response and the second loopback responsecomprises multiplying at least one of a transmit signal or a receivesignal, and the loopback response change.
 18. A non-transitorycomputer-readable storage medium comprising instructions that, whenexecuted, cause a machine to: measure a first loopback response of aradio-frequency (RF) subsystem for a first calibration configuration ofthe RF subsystem; measure a second loopback response of the RF subsystemfor a second calibration configuration of the RF subsystem; and adjustat least one of a transmit programmable shifter or a digital front endbased on a difference between the first loopback response and the secondloopback response to compensate for a loopback response change when theRF subsystem is changed from the first calibration configuration to thesecond calibration configuration.
 19. The non-transitorycomputer-readable storage medium of claim 18, wherein the firstcalibration configuration of the RF subsystem comprises a currentcalibration configuration of a transmit channel, and a currentcalibration configuration of a receive channel, the second calibrationconfiguration is the current calibration configuration of the transmitchannel, and a new calibration configuration of the receive channel, andthe difference between the first loopback response and the secondloopback response represents a change in the receive channel.
 20. Thenon-transitory computer-readable storage medium of claim 18, wherein thefirst calibration configuration of the RF subsystem comprises a currentcalibration configuration of a transmit channel, and a currentcalibration configuration of a receive channel, the second calibrationconfiguration is a new calibration configuration of the transmitchannel, and the current calibration configuration of the receivechannel, and the difference between the first loopback response and thesecond loopback response represents a change in the transmit channel.21. The non-transitory computer-readable storage medium of claim 18,wherein the first calibration configuration of the RF subsystem is acurrent calibration configuration of a transmit channel of a firstsystem-on-a-chip device, and a current calibration configuration of areceive channel of a second system-on-a-chip device, the secondcalibration configuration of the RF subsystem is a new calibrationconfiguration of the transmit channel of the first system-on-a-chipdevice, and the current calibration configuration of the receive channelof the second system-on-a-chip device, and the difference between thefirst loopback response and the second loopback response represents achange in at least one of the transmit channel, or a common mode path.